SARS-CoV-2 spike antigen quantification by targeted mass spectrometry of a virus-based vaccine

•The spike glycoprotein of SARS-CoV-2 mediates virus binding to host cells’ receptors and is a key target for vaccines development.•The spike induces a specific immune response. Yet, no method was developed for spike quantification.•A mass spectrometric based method for spike quantification was developed and demonstrated on spike-based vaccine.•Proof of concept of this method is shown for complex matrix samples and total spike levels were correlated with results from activity assays.•The method is simple, reliable and allows determination of antigen quantity within a sample, and can be easily implemented for any vaccine or therapeutic sample.